This invention relates generally to flat panel display devices, and more particularly to panel structures for flat panel display devices.
A flat panel display device responds to a video signal to form an image on a screen. Such devices are used in conjunction with a host device which generates the image signal. Exemplary host devices are a computer, a calculator, a telephone, a hand-held device or other appliance. A large commercial use for the flat panel display is to serve as a computer display in place of a large and heavy cathode ray tube (CRT) display. A flat panel display, such as a liquid crystal display (`LCD`) or a field emission display, is relatively light weight and consumes less power compared to the cathode ray tube. Such characteristics are particularly desirable for portable computing device displays, where light weight and low power are important attributes.
An LCD generally includes a backplate substrate, a faceplate substrate and a liquid crystal material sealed between the two. The liquid crystal is an oily substance that flows like a liquid, but has a crystalline order in the arrangement of its molecules. An electrical field is applied to thread-like or pneumatic liquid crystal molecules which respond by reorienting themselves along electric field lines. Such orientation of the molecules causes light to be transmitted or blocked. The backplate typically is a glass substrate on which are formed a horizontal scanning circuit, a vertical scanning circuit and a pixel region. For an active matrix LCD, the glass substrate is essentially a large integrated circuit having millions of thin-film transistor (TFT) switches. The TFT switches form horizontal and vertical scanning circuits. To fabricate the backplate, glass is poured defining an extremely flat substrate. The glass substrate is purified of alkali metals, which might contaminate the transistors or the liquid crystal. A thin film layer of semiconductive material then is deposited by a plasma process which condenses a random network of silicon, rich in hydrogen, onto the glass. Finally, metal electrodes, insulators and other elements are deposited in a manner similar to the fabrication of integrated circuits to define the TFT switches.
The faceplate typically includes electrodes to complete the TFT circuit paths. The faceplate also includes light polarizers and color filters. The LCD panel further includes a light source for providing backlighting. The liquid crystal material, along with a spacing medium, are sealed between the faceplate and the backplate by a glue around the periphery of the plates. The spacing medium typically is formed of very small spheres or fibers that, prior to gluing the plates together, are adhered to the underside of the faceplate by static electricity. The distance between the plates is determined by the diameter of the spheres. The TFT switches define respective cells of a pixel region. Each cell serves as a color pixel. Alternative LCD displays are formed by passive matrix designs formed with `super twist` or `double super twist` switches. A major distinction between active matrix LCDs and passive matrix LCDs are that passive matrix LCDs do not have a transistor associated with, and located with, each pixel.
A field emission display (`FED`) includes a faceplate and a backplate spaced apart and sealed to define an intermediary vacuum envelope. The interior surface of the faceplate typically is coated with light emissive elements, such as phosphor or phosphor patterns, which define an active region of the display. Field emitters, or cathodes, are formed on the backplate. A gate electrode located on the backplate is associated with the emitters. When a sufficient voltage differential is established between the emitters and the gate electrode, a Fowler-Nordheim electron emission is initiated from the emitters. The released electrons are accelerated toward the phosphor regions, or anodes, on the faceplate. The electrons strike the phosphor causing the phosphor to emit photons. Emitted photons are intended to strike only certain targeted phosphors. Generally there is a one to one correspondence between each emitter (cathode) and phosphor (anode). A pixel is formed by one or more of such emitter and phosphor sets.
Conventionally an interelectrode spacer is used to separate the baseplate and faceplate. Such spacer also serves as an insulator preserving the voltage difference between the emitter and phosphor. U.S. Pat. No. 5,503,582 discloses a substrate between the faceplate and backplate having openings. The substrate serves as a spacer and insulator structure. U.S. Pat. No. 5,656,887 discloses a microchannel plate located between an emitter plate and a screen assembly. The microchannel plate includes a dielectric plate in which a large number of cylindrical passageways, or microchannels, are formed.
As described above, the conventional backplate and faceplate of an LCD panel or an FED panel is made from glass. One shortcoming of glass panels is that the glass is breakable. Another shortcoming is that the glass is relatively heavy. These shortcomings are more pronounced as flat panels are developed with larger viewing areas and lighter weight. To reduce weight the panels are made thinner. As the area of a glass panel increases and as the thickness of such panel decreases, the glass panel becomes undesirably more fragile. Another shortcoming of glass is that the manufacturing processes tend to result in glass panels of varying, rather than uniform, thickness. This is undesirable because varying thickness along the viewing area introduces varied refraction of display light. Accordingly, it is desirable to achieve a lighter flat panel display which is less fragile and more precisely manufactured to desired tolerances.